In a commercial refrigeration system, a compressor rack represents one of the most expensive part of the system. Consequently, the effective operation of a compressor rack can be very important. One of the commonly used control optimality measures directly related to compressor rack operation can be the rate of change typically derived from a suction pressure measurement. The aim is usually to keep the suction pressure rate of change value within a reasonable range since it directly corresponds to the switching/staging rate in a parallel compressor rack. However, even if a system maintains the suction pressure rate of change within a reasonable range, there is no drill down capability, that is, there is no information about the load distribution among the individual compressors in the rack.
Moreover, in vapor-compression systems, compressor-related faults represent the largest part of service costs. Faults typically related to a reciprocating compressor in the rack can be divided into two major groups according to their impact on an individual compressor amp draw. First, there are faults resulting in a higher amp consumption (mechanical faults, e.g. increased friction), and second, faults resulting in an amp consumption decrease (e.g., a valve leak) in comparison with the referential value obtained under same driving conditions. Both types of faults cause an efficiency decrease of the compressor. Early diagnostics in commercial refrigeration systems can reduce the equipment downtime as well as service costs. Approaches presently available however cannot be applied to an individual compressor operating in a compressor rack. The available approaches consider either a simple single compressor system or monitor the whole compressor rack performance. So as noted above, drill-down capability (fault diagnostics) is somewhat limited. The other group of approaches is based on additional (and rarely available) information from the compressor manufacturer (e.g., so-called compressor maps).